Meanders

• What is a meander?

  A bend in a river caused by erosion
• Explain how meanders are formed (6 marks)

  • Meanders are formed in the middle course of a river.
  • As the river gains more velocity, the water is pushed to the outside of the river causing more erosion on the outside bend, which forms a steep river cliff.
  • This is achieved through processes like hydraulic action and abrasion. Water on the inside of the bend of the river has a lower velocity because there is more friction.
  • Therefore, the water starts to deposit eroded materials like sand and shingle, consequently creating a slip off slope
• How are meanders formed?

  • Water flows slowly over shallow areas of the river bed (riffles) and faster in the deeper sections (pools)
  • Sediment is then deposited on the inside bend (due to friction slowing down the velocity) forming a slip off slope
  • Faster flowing water on the outside bend causes lateral erosion (abrasion and hydraulic action) which undercuts the bank and forms a river cliff
  • This starts a cork-screw like flow (helicoidal flow) from one side of the bank to the other

  
• What is the Cross Profile of a Meander?

  The cross profile of a meander shows how the river channel changes across a bend due to erosion and deposition
• Cross Profile – Outer Bend (Erosion Zone):

  • Outer bend experiences fast-flowing water, leading to hydraulic action and abrasion, which erode the bank.
  • This forms a steep river cliff and makes the water deeper here.
• Cross Profile – Inner Bend (Deposition Zone):

  • At the inner bend, the water moves slowly, causing deposition.
  • Sediment builds up to form a slip-off slope, and the water is shallower here
• Cross Profile – Thalweg (Fastest Flow of Water)

  • The thalweg is the fastest-flowing section of the river.
  • It follows the outer bend, where erosion is strongest
• How Does the Cross Profile Change Over Time in a meander?

  As erosion deepens the outer bend and deposition builds up the inner bend, the meander becomes more exaggerated over time.